(1) Field of the Invention:
The present invention relates to an active matrix drive type liquid crystal display apparatus using thin film transistor (TFT), and manufacturing method therefor.
(2) Description of the Prior Art:
In an active matrix type liquid crystal display apparatus, switching elements are provided corresponding to respective of plural pixel electrodes arranged in a matrix. In the active matrix type liquid crystal display apparatus, liquid crystal at respective pixel is always driven theoretically, and contrast is higher than that of a simple matrix type display apparatus which uses time division drive system. Therefore, the active matrix type technology is indispensable especially for color display.
In accordance with prior art of the active matrix type liquid crystal display apparatus, thin film transistor (TFT) is composed by being provided with an insulating transparent substrate, whereon a gate electrode (gate line), a gate insulating film, a semiconductor layer, a drain electrode (data line), and a source electrode are provided orderly. Transparent electrodes are connected to the source electrode. The structure of TFT wherein gate electrodes are formed first on the substrate is generally called an inverted staggered structure. JP-A-61-161764 (1986) disclosed such a TFT.
The liquid crystal display apparatus using TFT is characterized in having high contrast because it is capable of active drive. However, the process for forming a TFT on the substrate is complex, and generally it requires six or more steps of photolithographic process (hereinafter called photo-treatment). When the number of the photo-treatment steps for manufacturing the TFT substrate is large, there are problems such that manufacturing cost of the TFT substrate increases, and further, a production yield of the manufacturing decreases on account of contamination with dust which comes from outside or being generated at the manufacturing process.
One of the methods for simplifying the process, a prior art is disclosed wherein a gate insulating film and a semiconductor layer, and metallic film to be drain electrodes and source electrodes are formed continuously, the semiconductor layer is manufactured as a mask for the metallic film, and subsequently a transparent electrodes are formed.
However, a problem has been generated such that the transparent electrodes are readily broken by a step which is formed by a remained eaves shaped end portion of the source electrode if etching speed of metallic film composing the source electrodes is slower than etching speed of the semiconductor layer when the etching process of the semiconductor layer. That means, the production yield of the TFT substrate has not been considered sufficiently.
In order to realized bright display image, an area of light transmitting portion of the transparent pixel electrode (hereinafter called aperture ratio) must be as large as possible. However, in accordance with the above prior art, increase of the aperture ratio for realizing bright display image has not been considered sufficiently.
Further, at a ride over portion of the gate electrode in the TFT semiconductor pattern, a breakage is generated in the semiconductor pattern because an end portion of the semiconductor pattern has faster etching speed than flat plain portion, a leak electric current between the semiconductor layer and the gate electrodes increases. Accordingly, it has been a problem that a short circuit (G/D short) among the source electrodes, the drain electrodes, and the gate electrodes which are formed on the semiconductor pattern is readily generated.